CP violation in oscillations measured with the BaBar experiment

1
CP violation in oscillations measured with the
BaBar experiment

• Riccardo Faccini
• Univ. La Sapienza INFN Roma
• Les recontres de Physique de la Vallee dAoste
• March 9-15, 2003

(r,h)
a
g
b
(1,0)
(0,0)
2
The Triangle
Bd system

• CKM matrix is unitary

(r,h)
VtbVtd VcbVcd
VubVud VcbVcd
a
phases ? angles ?(f2), ?(f1), and ?(f3)
b
g
(1,0)
(0,0)
CP violation proportional to triangle
area measure sides and angles independently
3
CP violation in mixing and decay

• Consider B decays to a mode f
• interference between mixing and decay

mixing
f is not necessarily a CP eigenstate
decay
Mixing phase
Examples
4
CP parameters

• l?1 if direct CP Violation
• If f is a CP eigenstate, only one l fit for
  l and Im(l) or for
• If f is not a CP eigenstate , need also
• 5 parameters ACP and

and
and
direct CPV
CPV in mixing
5
Measurements of b
Charmonium K0 Penguin and tree have the same weak
phase
J/Y
c
c
B0
K0
d
d
d
d
D()D() and J/Yp0 Penguin and tree have
different weak phases asymmetry not necessarily
sin2b
D()
c
c
D()-
B0
d
d
d
d
fK0 and h()K0 Mostly penguin. In principle
measures sin2b, but sensitive to new physics
f
s
K0
d
d
6
Measurements of a
pp- , rp- , pp-p0 Penguin and tree have
different weak phases asymmetry measures sin2aeff
p
u
u
p-
B0
d
d
d
d
From sin2aeff to sin2a

• pp- , rp- require isospin analysis (see talk
  from S. Laplace)
• Long term3-body dalitz analysis. Penguin to Tree
  ratio is fit in each point of the Dalitz plot

7
Measurements of sin(2bg)in B0?D-p,r,a1
d
D()-
A
A
p
u
b
u
B0
B0
p
D()-
d
d

• g enters via the Cabibbo suppressed amplitude A.
  
• Small asymmetry l0.02
• need to measure l ? measure BF (B0 ? Ds p-)

s,d
Ds,D
c
BF (B0 ? D- p)
fDs2
p-
B0
BF (B0 ? Ds p-) ?
? l2Dp
d
d
tan2qC
fD2
Dr,a1 more complicated but will not require l
(angular analysis)
8
Analyses presented on 88M BB decays (run12)
collected by the BaBar experiment _at_ PEP-II
Experimental Technique
B-Flavor Tagging
Exclusive B Meson Reconstruction
Accurate and unbiased measurement of the vertices
Low BR (10-5) means high luminosity
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Tagging and Vertexing

• Leptons and Kaons sign tags B flavor
• t
• Dz resolution 180mm

Tagging efficiency and vertex resolution measured
from the data
10
sin2b in b?csc
Charmonium K0 Penguin and tree have the same weak
phase
J/Y
c
c
B0
K0
d
d
d
d
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• Charmonium states

hCP 1 B0 ? J/? K0L
hCP -1 B0 ? J/? K0S B0 ? ?(2s) K0S B0 ?
cc1 K0S B0 ? hc K0S
hCP (1-2RT) B0 ? J/? K(K0Sp0)
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Fit results
hCP -1
hCP 1
sin2b 0.755 ? 0.074
sin2b 0.723 ? 0.158
sin2b 0.741 ? 0.067 (stat) ? 0.034 (sys)
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sin2b fit results by decay mode
Direct CP search yields no evidence l 0.948
? 0.051(stat) ? 0.030 (syst)
Consistency of CP Channels P(c2) 57
14
sin2b in b?cdc
D()D() and J/Yp0 Penguin and tree have
different weak phases asymmetry not necessarily
sin2b
D()
c
c
D()-
B0
d
d
d
d
15

• DD-, is not a CP eigenstate (L0,2 and L1)
• CP odd fraction R ?
• .Transversity analysis

• B0?D D-

CP-odd fraction R ? 0.07 ? 0.06 ? 0.03
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sin2b from B0?DD-
If no penguins we should measure Im(l)-sin2b
B0 ? DD-
We also measure l
From 126 ? 12 signal events
Im(l) 0.31 ? 0.43 (stat) ? 0.13 (syst)
-sin2b -0.741 ? 0.067 l 0.98 ? 0.25
(stat) ? 0.09 (syst)
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sin2b from B0?DD-
In SM with no penguins S-S- -sin2b
C-C-0
Not a CP eigenstate use the S C
parametrization Vector-PseudoScalar no angular
analysis required
S- -0.24 ? 0.69 ? 0.12 C- -0.22 ? 0.37 ?
0.10 S- -0.82 ? 0.75 ? 0.14 C- -0.47 ? 0.40
? 0.12
B ?DD-
B ?D-D
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B0 ? J/y p0
40?7 events
If no penguins we would measure S-sin2b
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sin2b in b?sss
fK0 and h()K0 Only penguin. In principle
measures sin2b, but sensitive to new physics
f
s
K0
d
d
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Penguin dominated (quark composition unknown)
hKs
h? rg
h? hpp
-S 0.020.340.03sin2b in SM (no Tree)
N.B. Charmonium modes 0.741 0.067
fKs
-S-0.190.520.09 sin2b in SM
Assuming l1
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sin2a in b?udd
pp- , rp- , pp-p0 Penguin and tree have
different weak phases asymmetry measures sin2aeff
p
u
u
p-
B0
d
d
d
d
22
sin2aeff from B ? pp

• Analysis proceeds in two steps
• Time-independent fit for yields and Kp charge
  asymmetry (see talk from S. Laplace)
• Time-dependent fit for S, and C

23
Taming the Penguins Isospin Triangle

• Triangle relations allow determination of
  penguin-induced shift in a (see talk from S.
  Laplace)

Br(B?pp0)106
ACP
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CP-Violating Asymmetries in B0 ? rp-, rK-

• Much more difficult than pp-
• Three-body topology with neutral pion
  (combinatorics, lower efficiency)
• Significant fraction of misreconstructed signal
  events and backgrounds from other B decays
• Need much larger sample than currently available
  to extract a cleanly
• We perform a quasi-two-body analysis
• Select the r-dominated region of the
  pp-p0/Kp-p0 Dalitz plane
• Use multivariate techniques to suppress qq
  backgrounds
• Simultaneous fit for rp- and rK-

25
Yields
B0? rp time-dependent asymmetry
hep-ex/0207068
BB and qq
Preliminary
Systematic error dominated by uncertainty on B
backgrounds
26
sin2bg in b?cdd
A
A
p
p-
u
c
B0
B0
D()-
D()
d
d
d
d
Ready to measure on run1run2 l already
determined _at_ 30 level from
BF (B0 ? D- p)
fDs2
BF (B0 ? Ds p-) ?
? l2Dp
tan2qC
fD2
27
B0 ? Ds p- yield
14.9 ? 4.1 events
D- r
D- p
Evidence of reflected Ds?D background

• Systematic error mostly from uncertainty on BF of
  secondary decays, peaking background uncertainty,
  selection criteria

significance of the signal 3.5 s
BF( B0 ? Ds p- )() ( 3.1 ? 1.0 ? 1.0 ) ?
10-5 BF( B0 ? Ds p- ) ? BF(Ds ? f p ) (
1.11 ? 0.37 ? 0.24 ) ? 10-6
() 25 uncertainty from PDG BF(Ds ? f p)
l0.0200.005(stat.sys.) 0.007 (th.)
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Sum

• Starting to measure direct CPV and sin2aeff in
  b?uud transitions
• If it werent for penguins s(sin2a)0.2 ?
  isospin triangle desperately needed so far

B0? rp
B0? pp
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mary

• sin2b starts to be measured in a lot of different
  environments
• Ignoring penguins, within the SM ?
• Hints for interesting developments?

sin2b
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Backup slides
31
BaBar and PEP-II _at_ SLAC

• High luminosity asymmetric B factory _at_ ?(4S)
• 9 GeV e- on 3.1 GeV e
• ?(4S) boost ltbggt ? 0.55

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PEP-II performances

• 24 fb-1 in run 1
• 70 fb-1 in run2
• 10 fb-1 so far in run3

run3
Analyses presented on 88M BB decays (run12)
run2
(12 off peak)
run1